Thanks to the advantage of low costs and readily accessible in application, organic solvents and compounds are commonly used in an array of processes in various fields, including petrifaction, dyeing and finishing, semiconductor, and nuclear industries. However, it is inevitably to leave behind secondary waste such as organic wastewater, spent ion exchange resin. The organic waste needs to be further treated to meet the requirements of regulations for environmental protection before discharged so that it will not pose a threat to the surroundings.
A host of technologies for the treatment of organic waste have been developed and proposed worldwide and some of them are even successfully applied commercially. Some approaches employ extraction to separate organic components from original wastewater for reusing. Other processes decompose the organic components in the waste via addition of oxidants or degrade organic parts more efficiently by means of advanced oxidation. Still others destroy organic waste thoroughly via incineration and pyrolysis. Nonetheless, addition of extra oxidants is inherently to generate secondary waste. Besides, the oxidation efficiency declines substantially when the composition of waste is complex. In the case of advanced oxidization methods such as Fenton reaction, the catalyst—ferrous ion is likely to be consumed and cannot be recycled in each batch of reactions. Moreover, ferric hydroxide precipitates out and additional separation devices are required when the solution is alkaline. On the other hand, if incineration or pyrolysis is employed to treat organic waste, auxiliary fuel should be added because of insufficient calorific value. Moreover, the operation and maintenance costs are high. Thereby, the treatment of organic waste demands a better option.
In order to address the problems suffered in the above methods, a unique magnetic catalyst is developed for the treatment of organic waste in the Fenton reaction. In addition to the efficiency of decomposing organic waste comparable to that of Fenton reaction according to the prior art, the catalyst can also be readily recycled and no secondary waste in existence in the process.
The Fenton reaction is the process of mixing hydrogen peroxide with ferrous ions under acid conditions. It produces hydroxyl radicals (.OH) with strong oxidizing ability, which can further oxidize organic compounds. According to the Taiwan patent publication number I262174, ferrous ions in aqueous solutions are used as the catalyst for oxidation reaction to decompose the organic compounds in water. Nonetheless, in the reaction, the ferrous ions are prone to transform into ferric ions, which tend to form ferric hydroxide that readily precipitates out in neutral or alkaline environment. Accordingly, not only does secondary waste need to be dealt with, the treatment costs also increase as well.
Furthermore, as disclosed in the Taiwan patent publication number 309506, metal iron at the anode of an electrolytic/oxidizing reactor is oxidized while ferrous ions form at the cathode. Then add hydrogen peroxide for oxidizing the organic components in wastewater to decrease the level of chemical oxygen demand (COD) and avoid secondary waste coming from slurry of iron. Nonetheless, this technology only gears toward the treatment of organic wastewater with COD less than 1000 mg/L. Besides, extra electrolytic devices are required and the establishment of the system appears to be demanding. The capital and maintenance costs also increase.
Moreover, Taiwan patent publication number 524779 illustrates a technology of chemical oxidizing treatment for wastewater to yield only minor sludge. The ferric salts produced from the Fenton reaction tend to settle on the surface of the substrate in a fluidized bed. Thereby, over a half amount of sludge can be avoided in the solution. Nonetheless, this method merely applies to the treatment of organic wastewater with total organic carbon (TOC) less than 100 mg/L. Besides, its TOC-removing efficiency is only about 50%. The process is not suitable for the treatment of wastewater with high concentration of organic compounds.
In addition, according to the advanced oxidation process of iron-series catalysts disclosed in the Taiwan patent publication number I355294, by using heterogeneous and homogeneous iron ion catalysts simultaneously, the formation of free radicals from ozone is enhanced and thus reducing the total concentration of organic carbon in solution. However, this system needs the application of both technologies of ozone and ultraviolet-ray oxidation. Extra devices such as ozone generator and ultraviolet-ray lamps are also required. The whole process comes with complex operating procedures and demands special skills to operate and maintain. Only cases for the treatment of organic wastewater with low concentration are available.
Accordingly, the present invention try to provide a catalyst that can be applied extensively for the treatment of various organic wastes in Fenton reaction.